Issue No.03 - May/June (2001 vol.21)
There is an important distinction between wearable devices and those that are merely portable, the classic example being the pocket watch and wristwatch. The difference is simple: You have to pull out the pocket watch and open it to see the time, while the wristwatch enables you to see the time instantly, even while working with both hands.
Alex (Sandy) Pentland, "Guest Editor's Introduction: Wearable Information Devices", IEEE Micro, vol.21, no. 3, pp. 12-15, May/June 2001, doi:10.1109/MM.2001.928761